Comparative study of Cu2+ adsorption on a zeolite, a clay and a diatomite from Serbia

The adsorption of a zeolite, clay and diatomite from Serbia toward aqueous Cu2+ ions was studied, at different pH. The adsorbents were characterized with respect to phase composition, specific surface area and point of zero charge. The amounts of Cu2+ removed from the solution, increased with increasing initial pH, reaching nearly 100% at pH > 7, regardless of the adsorbent type and metal concentration, due to precipitation of Cu(OH)2. Relatively constant final pH values and less significant increase of Cu2+ uptake observed in the initial pH range 4–6 have pointed out the role of buffering properties of investigated adsorbent materials. The maximum adsorption capacities decreased in the order zeolite (0.128 mmol/g) > clay (0.096 mmol/g) > diatomite (0.047 mmol/g). The Langmuir equation was most suitable for data fitting. The proportion of Cu2+ desorbed in acidic media decreased with the increase of previously adsorbed amounts by zeolite and clay, while the opposite was true for diatomite. Ion exchange of exchangeable cations and protons were identified as main adsorption mechanisms, with latter being most apparent in the removal mechanism of diatomite. Considering low-cost, local availability and environmentally friendly materials, zeolite exhibited highest potential for environmental and health protection applications.